A flowability of simple liquids, for example, such as water, alcohol, glycerine or the like, is different in viscosity, but these liquids exhibit a Newtonian viscosity, that is, a straining rate proportional to a stress during the flow. On the other hand, it has been known that thick liquids having a relatively complicated construction, for example, such as paint, toothpaste, mayonnaise and cold cream, exhibit a non-Newtonian viscosity which will not start the flow unless an external force exceeds a predermined value. On the other hand, the property of gels which change into sol when subjected to shaking or vibration, and then return again to gels when left standing is called thixotropy.
A measurement of Newtonian viscosity or non-Newtonian viscosity, particularly, the degree of thixotropy, can be determined by evaluating an area of a hysteresis loop based on the number of revolutions of a rotary viscometer. In the rotary viscometer, the viscosity is obtained by rotating a cylindrical body in a viscous fluid and measuring a torque due to the viscosity exerted on the cylindrical body. In a coaxial double cylindrical meter, a fluid is put between an inner tube and an outer tube, and a torque exerted on the inner tube when the outer tube is rotated is measured. This measurement is carried out by hanging the inner tube by means of a torsion wire and obtaining a torsional angle of the torsion wire. If a design is made so that an angular velocity of a rotary body is made variable so as to vary a shear rate corresponding thereto, it can be applied to the measurement of the flow characteristics of non-Newtonian viscous fluids.
However, it is necessary to vary the shape of a rotary body depending on a sample to be measured. Furthermore, since it is cumbersome to clean and wash the rotary body after being used, a problem arises in handling and using the apparatus. In addition, being affected by the inertia of the rotary body or by the flow of the sample, the range of a controllable angular velosity of the rotary body is narrow, and various measuring patterns cannot be selected.